1. Field of the Disclosure
The disclosure relates to an automotive V-belt nonstage transmission for a vehicle, such as a motorcycle or an all-terrain four-wheel vehicle.
2. Description of the Related Art
An automotive V-belt nonstage transmission of the kind is required, in view of improving the operability of a vehicle, to have a clutch function to prevent the excessive creeping of the vehicle while an engine mounted on the vehicle is idling, and an engine-brake effectuating function to effectuate engine brake while the engine is idling. Various V-belt nonstage transmissions capable of effectuating engine brake when necessary to meet both those requirements have been developed. FIGS. 7 and 8 show such a known V-belt nonstage transmission.
Referring to FIG. 7, the known V-belt nonstage transmission is provided with a drive pulley 1 capable of serving as a clutch and including a drive shaft 6 coupled with a crankshaft 5 included in an engine, a fixed sheave 10 fixedly mounted on the drive shaft 6, and a movable sheave 11 axially movably mounted on the drive shaft 6. The fixed sheave 10 and the movable sheave 11 have conical pressure surfaces 10a and 11a, respectively. The conical pressure surfaces 10a and 11a define a V-groove 19. The outer surface 6a of the drive shaft 6 serves as the bottom surface of the V-groove 19. A disk-shaped support member 30 is connected to the back surface of the movable sheave 11 by a connecting arm 31. A flyweight mechanism 9 includes flyweights 37, a spider 38 and rollers 39. The spider 38 is screwed on the drive shaft 6 and is engaged circumferentially with the connecting arm 31. Thus, the movable sheave 11 rotates always together with the drive shaft 6. The flyweights 37 are pivotally supported on the movable sheave 11 by pins 41 so as to be radially swingable on the pins 41 and in contact with the rollers 39. A return coil spring 42 is compressed between the spider 38 and the support member 30 to push the movable sheave 11 in an expanding direction to expand the V-groove 19, i.e., to the right. The support member 30 is mounted on a bearing metal 33 put on the drive shaft 6 so as to be axially movable on the drive shaft 6. A bearing 80 is fitted in the boss of the support member 30, an annular plate 82 is placed in contact with the boss of the support member 30 via the bearing 80, and a control lever 81 for controlling engine brake is disposed opposite to the annular plate 82. The outer most position, i.e., the right end position as viewed in FIG. 7, of the support member 30 can be adjusted by the control lever 81.
While the engine is idling, the control lever 81 is moved to the right to separate the pressure surface 11a of the movable sheave 11 from a side contact surface 3a of a V belt 3 as shown in FIG. 7. In this state, the clutch is disengaged. When the vehicle runs down a slope with the engine operating at an idling speed, the control lever 81 is shifted in a narrowing direction to narrow the V-groove 19, i.e., to the left to compress the V belt 3 between the respective pressure surfaces 10a and 11a of the fixed sheave 10 and the movable sheave 11 of the pulley 1, so that engine brake is effectuated.
Referring to FIG. 8 showing a lever type engine brake control mechanism for operating and controlling the control lever 81, a lever support shaft 100 has one end part on which the control lever 81 is mounted and the other end part on which a swing link 101 is fixedly mounted. A torsion coil spring 102 wound around the lever support shaft 100 presses the control lever 81 against the annular plate 83 so that the movable sheave 11 is pressed against the V belt 3 to compress the V belt 3 between the fixed sheave 10 and the movable sheave 11. A collar 107 attached to the swing link 101 is engaged with an eccentric output shaft 106 of an electric motor 105. A control unit 110 has an output part connected to the electric motor 105, and an input part connected by a cable to a speed sensor, not shown, a traveling direction sensor, not shown. A V-belt nonstage transmission provided with a cam-and-lever type engine brake system is disclosed in JP11-165686A instead of the lever type system described above.
Another known automotive V-belt nonstage transmission disclosed in Japanese Patent No. 2620490 is provided with a drive pulley having a fixed sheave connected by a one-way clutch to a drive shaft, a movable sheave, a clutch mechanism disposed between the fixed and the movable sheave, and an auxiliary coil spring for keeping the cutch mechanism engaged. The clutch mechanism is engaged and disengaged by the axial movement of the movable sheave of the drive pulley.
The V-belt nonstage transmission provided with the lever type engine brake control mechanism as shown in FIGS. 7 and 8 has the following problems.
(1) The control lever 81 and the associated parts must be formed in high dimensional accuracies and must be processed and assembled very accurately, which increases the manufacturing cost.
(2) The V-belt nonstage transmission needs many additional parts including the electric motor 105, i.e., an actuator, and the control unit for controlling the electric motor 105, which increases the cost of the V-belt nonstage transmission.
(3) Since those additional parts are disposed around the drive pulley, a large space must be formed around the drive pulley, which unavoidably enlarges the V-belt nonstage transmission.
The V-belt nonstage transmission disposed in Japanese Patent No. 2620490 has the following problems.
(1) The clutch mechanism engages gradually and hence it is difficult to determine a clutch engaging engine speed accurately, and dogs of the clutch mechanism strike against each other to generate unpleasant mechanical noise.
(2) The clutch mechanism is liable to disengage if the resilient force of the auxiliary coil spring for keeping the clutch mechanism engaged is small, and the auxiliary coil spring affects speed change ratio if the resilient force of the auxiliary coil spring is increased.